Fire retardant barriers are desirable for a wide variety of applications. Products for household and public occupancies such as health care facilities, convalescent care homes, college dormitories, residence halls, hotels, motels and correctional institutions are sometimes governed by regulations which require certain FR characteristics, particularly in bedding and upholstery. Fire barrier components are also needed in apparel, fire safety gear, vehicle and aircraft seating and walls, as insulators for appliances, walls, ducting, as barriers to separate sensitive controls from a heat source and other similar applications where fire safety is a concern. Effective fire barriers minimize the amount and rate of heat released from the barrier upon contact with fire. The rate of heat released is an indication of the intensity of the fire generated from the fire barrier material as well as how quickly the fire spreads. Slowing the spread of fire advantageously increases the amount of response time for a fire victim to safely escape and a fire department to successfully extinguish the fire.
In the bedding, upholstery and other industries, foams and nonwoven fibers are used in mattresses, sofas, chairs, and seat cushions, backs and arms. Traditionally, urethane foam has been combined with other types of cushioning materials such as cotton batting, latex rubber, and various nonwoven fibers in order to impart desirable comfort, loft and durability characteristics to a finished product. However, urethane foam is extremely flammable and must be chemically treated or coated to impart fire resistant properties thereto. As it is relatively fire resistant, neoprene foam is often used in bedding and upholstery products as well. However, as both neoprene foam and urethane foam which has been chemically treated to impart fire resistant properties thereto are relatively expensive, cost constraints may limit the applications for which neoprene foam and chemically treated urethane are commercially suitable.
Synthetic and natural nonwoven fibers have also demonstrated usefulness in the construction of mattresses and upholstery. Such fibers are inherently lightweight and therefore easy to ship, store and manipulate during processing. Rather than burning when subjected to open flame, many synthetic fibers, particularly polymer fibers and, more specifically, dry polyester fibers, tend to melt and drip. Furthermore, polymer fibers can be coated in a manner which enhances their tendency to resist burning. For example, polymer fibers which have been sufficiently treated such that they are considered to be non-flammable include Trevira CS, Kevlar® and Nomex®. Trevira CS is manufactured by Trevira Gmbh of Hatttersheim, Germany while both Kevlar® and Nomex® are manufactured by E.I. du Pont de Nemours and Company of Wilmington, Del.
Another fire resistant fiber is known as oxidized polyacrylonitrile (“PAN”). While fire resistant, however, oxidized PAN fibers are difficult to process into batts for use as a barrier layer and/or filling, particularly in bedding and upholstery applications. The oxidized PAN fibers are relatively low in weight and specific gravity, thereby making traditional carding methods used to form batts difficult. In addition, oxidized PAN fibers are often referred to as “dead” fibers because of their lack of resilience, loft and compressibility. As a result, oxidized PAN fibers are often unsuitable for use in applications, for example, bedding and upholstery applications, where comfort and loft are desired. Finally, because they are black in color, oxidized PAN fibers may be unsuitable in applications which require lighter colors underneath a light decorative upholstery or mattress layer.
International Publication No. WO 01/6834 A1, filed by the Assignee of the present application and previously incorporated by reference as if reproduced in its entirety, discloses a method of forming a fire combustion modified batt having a first, FR, layer formed from a blend of nonwoven and oxidized PAN fibers and a second layer formed from nonwoven fibers. The resultant batt has a distinctly gray colored side (the oxidized PAN layer) and a distinctly white side (the nonwoven fiber layer). The oxidized PAN layer acts as a flame barrier for the fire combustion modified batt while the nonwoven fiber layer acts as a sacrificial aesthetic layer which provides the fire combustion modified batt with a white surface. International Publication No. WO 03/023108 A1 discloses a nonwoven highloft flame barrier comprised of a blend of fibers which includes inherently flame retardant fibers, preferably, melamine fibers, either alone or in combination with other inherently flame retardant fibers, fibers capable of generating oxygen depleting gases, and low melt binder fibers.
What is sought are uni-layer and bi-layer fire FR nonwoven batts configured such that the use of various combinations of charring fibers characterized by a first flame response characteristic and oxygen-depleting fibers characterized by a second flame response characteristic combine to enhance the overall FR characteristic of the resultant FR nonwoven batt.